Implantable medical devices such as cardiac pacemakers and defibrillators have become widespread. One common approach of powering implantable medical devices includes a DC current supplied by a battery. One type of battery is known as a primary cell and is not rechargeable. The average lifetime of a primary cell battery is five years and requires an invasive procedure to replace the battery. Another type of battery, known as a secondary cell, is rechargeable. Secondary cell batteries may be recharged thousands of times but generally hold no more than a few weeks of power. A secondary cell battery may last up to twenty years.